1. Field of the Invention
The present invention relates to a photo-detective-type laser output measuring apparatus.
2. Description of the Related Arts
In the field of laser processing for example use has been made of laser output measuring apparatuses for detecting the output (beam intensity) of laser beams to provide automatic control of the processing qualities. In general the laser output measuring apparatuses are roughly divided into two types, that is, a calorie measurement type using photo-thermal converters such as calorimeters and a beam detecting type using photoelectric converting elements such as photodiodes. Recently prevailing is the beam detecting type from the viewpoint of response speed.
Inconveniently such type of photoelectric converting elements have photoelectric conversion characteristics varying depending on the temperatures, so that they may issue different output signals in spite of reception of beams having the same output. Therefore if the photoelectric converting elements are subjected to the influence of ambient temperatures (atmospheric or room temperatures) they will issue different output signals even though the laser beam outputs are the same between morning and daytime, resulting in different laser output measurement values.
Thus it is common to be provided with temperature control devices for keeping the photoelectric converting elements at certain temperatures without being influenced by the ambient temperatures. Existing typical temperature control devices comprise thermally conductive retainers each mounted with not merely the photoelectric converting element but also with a resistance heating element and a temperature sensor. Then the retainer is heated by heat generated by the resistant heating element through the supply of electricity thereto while simultaneously the temperature of the retainer is detected by the temperature sensor to provide on-off control of the heat generating action of the resistance heating element with the aim of keeping the temperature of the retainer at a certain value.
In the on-off-controlled temperature control devices as described above, heating (on) and cooling (off) actions alternate, with the result that disadvantageously the temperature of the retainer or the photoelectric converting element may fluctuate periodically in the vicinity of the set temperature and the resultant ripple may act adversely on the output signal of the photoelectric converting element and hence on the laser output measurement values.
One possible solution to this problem is to employ PI (proportional integration) control method or PWM control method as the control methods for temperature control. These control methods allow the resistance heating elements to generate heat continuously (without cease) to variably control the amount of heat generation thereof, thus providing ripple-free temperature controls.
However, both the methods include costly control circuits and hence will cause a rise in total costs unless specific measures are taken, lacking in cost effectiveness of the ripple prevention. In addition the PWM control method may generate noises in its high-frequency switching circuit which may get in the measuring circuit associated with the photoelectric converting element. This would also make it hard to employ the method.